Multi-phase voltage regulators are used in high-current and low voltage applications, typically 25-150 A and 0.8-1.2V. The main advantages for multi-phase voltage regulators are to lower the ripple at the output, to reduce the bulk capacitors at the input and the output, and to increase efficiency.
FIG. 1 shows a schematic diagram of a multi-phase switch-mode voltage regulator circuit 100 which includes a controller and n phases (11 to 1n) with each phase comprising a high-side metal oxide semiconductor field effect transistor (MOSFET) switch 101, a low-side metal oxide semiconductor field effect transistor (MOSFET) switch 102, a high side gate driver circuit 103 for switch 101, a low side gate driver circuit 104 for switch 102 and an inductor (L1 . . . Ln). The controller sends out gate drive signals to the high side gate driver circuits 103 and low side gate driver circuits 104 of all the phases. Each high side gate driver circuit 103 is connected in serial and controls the gate of a high side switch 101 to turn on or turn off the switch according to the gate drive signal. Each low side gate driver circuit 104 is connected in serial and controls the gate of the low side switch 102 to turn on or turn off the switch.
For the first phase 11 as shown in FIG. 1, the input terminal of high side gate driver circuit 103 receives an inverse gate drive signal PMW that drives the gate of high side switch 101. The input terminal of low side gate driver circuit 104 receives a gate drive signal PWM that drives low side switch 102. The high side gate driver circuit 103 and low side gate driver circuit 104 in FIG. 1 are inverters. Accordingly, high side gate driver circuit 103 turns on high side switch 101 at a logic Low of PMW with the gate of high side switch 101 pulled up to the voltage at the node BST1. Further, the high side switch 101 at a logic HIGH of PMW with the gate of high side switch 101 pulled down to the voltage at the node SW1. Meanwhile, when PMW is LOW, PWM is HIGH, and low side switch 102 is turned off. And low side switch 102 is turned on when PWM is LOW. The drain of high side switch 101 is connected to receive an unregulated input voltage VIN. The source of high side switch 101 is connected to the drain of low side switch 102 at the first switch node SW1. The source of low side switch 102 is connected to electrical ground GND. The voltage at SW1 is filtered by the inductor 105 and the output capacitor Cout and contributes to the output voltage Vout together with the other phases.
In the prior art, the gate driver circuits and the switches are laid out separately as discrete components. They are relatively large in order to carry the current required. Accordingly, the interconnection resistance and the gate coupling resistance capacitance product are high, which leads to low efficiency and large volume.
On the other hand, integrating a driver closely with the switch (DrMOS) reduces parasitic inductance and gate coupling resistance capacitance product, therefore improving efficiency of the converter. One DrMOS solution uses Multi-Chip Modules (MCM) as a well known technology which attaches the driver chip and the switch chip on a same lead frame to reduce parasitic inductance. However, this approach is not compact enough, and the current carrying ability is limited. Further, when the MCM solution for DrMOS is used in multi-phase systems, the size for the whole system is large.
Another difficulty with multi-phase systems is the increased cost, which is a result of multiple inductors, switches, input ceramic capacitors and large sized package. Thus, while keeping the advantage of multi phases, small size, high efficiency and low cost are also desired in multi-phase converters.